Geo: Avoid failed attachment sync entries when the `Upload` record does not exist

I assume this is a race condition like:

1. Create upload
2. The secondary schedules the upload to be synced
3. Delete project
4. The secondary fails to sync

These FileRegistry entries are actually already excluded from /admin/geo_nodes stats, so they are as good as marked as synced. They are basically orphans. We can get rid of them.

• In FileDownloadService, check for Upload record, and if it’s missing, don’t create a FileRegistry record at all
• Log what happened?

This is marked as technical debt because it isn't hurting anything. It's an easy fix though.